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The Vault
RowQ
The Vault
CBSE Class 11 Biology · 10 questions · 24 marks
Alongside the fast, wired signalling of the nervous system, the body runs a second, slower control network built entirely on chemical messengers released into the blood, and this chapter surveys it gland by gland. It covers how hormones are made, how they act on target cells often through receptors and second messengers, and works through each major endocrine gland in the human body along with the disorders that result when a gland makes too much or too little of its hormone.
The gland often called the 'master gland' because it regulates the activity of most other endocrine glands is the:
Answer
Pituitary gland is correct — its anterior lobe secretes tropic hormones such as TSH and ACTH that directly control the activity of the thyroid and adrenal cortex, and its close link with the hypothalamus lets it coordinate much of the endocrine system, earning it the name master gland.
Insulin, secreted by the beta cells of the islets of Langerhans, has the primary effect of:
Answer
Lowering blood glucose by promoting its uptake and storage is correct — insulin acts oppositely to glucagon, promoting the uptake of glucose into cells and its storage as glycogen, thereby lowering elevated blood glucose levels toward normal.
The hormone released from the adrenal medulla that prepares the body for a 'fight-or-flight' response by rapidly raising heart rate and blood glucose is:
Answer
Adrenaline is correct — released from the adrenal medulla during acute stress, it acts within seconds to raise heart rate, blood pressure and blood glucose, mobilising the body's resources for an immediate emergency response, unlike the slower-acting cortisol from the adrenal cortex.
Deficiency of iodine in the diet most directly impairs the synthesis of:
Answer
Thyroxine and triiodothyronine is correct — both major thyroid hormones require iodine as a structural component, so inadequate dietary iodine directly limits their synthesis, often causing the thyroid to enlarge (goitre) as it attempts to compensate.
Assertion (A): Steroid hormones such as cortisol can directly influence gene transcription inside a target cell. Reason (R): Steroid hormones are lipid-soluble and can diffuse across the cell membrane to bind receptors located in the cytoplasm or nucleus.
Answer
Both A and R are true and R is the correct explanation of A — because steroid hormones are lipid-soluble, they pass directly through the cell membrane rather than binding a surface receptor, and once inside they bind intracellular receptors that can act directly on DNA to regulate gene transcription, unlike protein hormones, which rely on surface receptors and second messengers.
Explain the antagonistic relationship between calcitonin and parathyroid hormone in regulating blood calcium levels.
Answer
Calcitonin, secreted by the thyroid gland, lowers elevated blood calcium levels, mainly by inhibiting the release of calcium from bone and reducing its reabsorption, so more calcium is deposited into bone or excreted. Parathyroid hormone (PTH), secreted by the parathyroid glands, has the opposite effect: it raises blood calcium levels when they fall too low by stimulating the breakdown (resorption) of bone tissue to release stored calcium, increasing calcium absorption from the intestine, and reducing calcium loss through the kidneys. Because these two hormones push blood calcium in opposite directions, their coordinated, antagonistic action keeps blood calcium concentration within the narrow range the body's cells require.
Distinguish between the hormones secreted by the anterior and posterior lobes of the pituitary gland, giving one function of each hormone mentioned.
Answer
The anterior pituitary itself synthesises and secretes several hormones under the control of releasing and inhibiting hormones from the hypothalamus: growth hormone (GH) stimulates overall body growth, particularly of bones and muscle; thyroid-stimulating hormone (TSH) stimulates the thyroid gland to secrete thyroxine; adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to secrete corticoids; follicle-stimulating hormone (FSH) and luteinising hormone (LH), together called gonadotropins, regulate the activity of the gonads; and prolactin (PRL) stimulates milk production in the mammary glands. The posterior pituitary, by contrast, does not synthesise its own hormones but stores and releases two hormones actually made by the hypothalamus: oxytocin, which stimulates contraction of the uterus during childbirth and ejection of milk during nursing, and antidiuretic hormone (ADH), which promotes water reabsorption by the kidney tubules, conserving body water.
Describe the structure and hormonal secretions of the adrenal gland, and explain how its two regions respond differently to stress.
Answer
Each adrenal gland, positioned above a kidney, is organised into two distinct regions with different embryonic origins and functions. The outer region, the adrenal cortex, secretes a group of hormones called corticoids. Glucocorticoids, mainly cortisol, help the body cope with prolonged stress by raising blood glucose levels (promoting the breakdown of proteins and fats to be converted into glucose), have anti-inflammatory and immune-suppressing effects, and help maintain cardiovascular function; mineralocorticoids, mainly aldosterone, regulate the balance of sodium and water in the body, mainly by promoting sodium and water reabsorption in the kidney, which helps maintain blood volume and blood pressure. The inner region, the adrenal medulla, is essentially a modified sympathetic nervous tissue and secretes the catecholamines adrenaline (epinephrine) and noradrenaline (norepinephrine) directly into the blood in response to sudden stress or danger. These hormones act within seconds, producing the classic fight-or-flight response: heart rate and the force of heart contraction increase, blood vessels supplying the skin and digestive organs constrict while those supplying skeletal muscle dilate, blood glucose rises rapidly as stored glycogen is broken down, and breathing rate increases, all of which prepare the body for immediate, vigorous physical action. Thus, while the adrenal medulla mounts an almost instantaneous response to acute, short-term stress, the adrenal cortex, through cortisol, supports the body's ability to cope with more prolonged or chronic stress by sustaining elevated blood glucose and modulating the immune response over a longer period.
Explain how the pancreas maintains blood glucose homeostasis, and describe what goes wrong in diabetes mellitus.
Answer
The pancreas functions as a mixed gland, with most of its tissue devoted to exocrine secretion of digestive enzymes, but scattered clusters of endocrine cells called the islets of Langerhans regulate blood glucose. These islets contain at least two important cell types: alpha cells, which secrete the hormone glucagon, and beta cells, which secrete the hormone insulin. When blood glucose rises after a meal, beta cells respond by secreting more insulin, which acts on target cells, particularly in the liver, muscle and adipose tissue, to promote the uptake of glucose from the blood into these cells and its storage as glycogen (in liver and muscle) or fat, thereby lowering blood glucose back toward the normal range. When blood glucose falls, for example between meals or during fasting, alpha cells secrete more glucagon, which acts mainly on the liver to stimulate the breakdown of stored glycogen back into glucose and its release into the blood, raising blood glucose back up. Through this continuous, opposing action of insulin and glucagon, the pancreas keeps blood glucose within a narrow, healthy range regardless of when a person last ate. Diabetes mellitus arises when this system fails, either because the beta cells produce too little insulin or because body cells fail to respond adequately to the insulin that is produced (insulin resistance); in either case, glucose is not taken up efficiently by cells, and blood glucose levels remain persistently elevated. Left uncontrolled, this chronically high blood glucose can damage blood vessels, nerves and organs such as the kidneys and eyes over time, and glucose may also appear in the urine as the kidneys are overwhelmed, which is why the disease is named after this feature (mellitus meaning 'sweet').
A child living in a mountainous region far from the sea shows a visibly swollen neck and appears sluggish and slow-growing compared to peers. A separate adult patient reports excessive thirst, frequent urination and unexplained weight loss over several months, and blood tests reveal persistently elevated glucose levels. (a) Identify the likely cause of the child's condition and explain why the geographic location is relevant. (b) Name the swelling seen in the child's neck and the gland responsible for it. (c) Identify the adult's condition and explain, in hormonal terms, why blood glucose remains elevated. (d) Suggest one measure that could help prevent the child's condition in populations living in similar regions.
Answer
(a) The child's condition is most likely caused by iodine deficiency, since iodine is an essential component of the thyroid hormones thyroxine and triiodothyronine; mountainous, inland regions far from the sea often have iodine-poor soil and water, and populations relying on local food sources in such regions are at higher risk of inadequate iodine intake. (b) The visible neck swelling is called a goitre, caused by enlargement of the thyroid gland as it grows larger in an attempt to compensate for insufficient iodine and produce adequate hormone. (c) The adult's symptoms and elevated blood glucose are consistent with diabetes mellitus. Blood glucose remains elevated because insulin, the hormone from pancreatic beta cells responsible for promoting glucose uptake into cells and its storage, is either insufficiently produced or the body's cells no longer respond adequately to it, so glucose accumulates in the blood rather than being taken up and used or stored by tissues. (d) Ensuring the population's diet includes iodised salt, which supplies a reliable source of dietary iodine regardless of local soil or water iodine content, is a well-established and effective public health measure to prevent iodine deficiency and the resulting goitre.
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